petsc-master 2014-10-21
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MatMFFDSetFunctionError

Sets the error_rel for the approximation of matrix-vector products using finite differences.

Synopsis

#include "petscmat.h"   
PetscErrorCode  MatMFFDSetFunctionError(Mat mat,PetscReal error)
Logically Collective on Mat

Input Parameters

mat - the matrix free matrix created via MatCreateMFFD() or MatCreateSNESMF()
error_rel - relative error (should be set to the square root of the relative error in the function evaluations)

Options Database Keys

Notes

The default matrix-free matrix-vector product routine computes
     F'(u)*a = [F(u+h*a) - F(u)]/h where
     h = error_rel*u'a/||a||^2                        if  |u'a| > umin*||a||_{1}
       = error_rel*umin*sign(u'a)*||a||_{1}/||a||^2   else

Keywords

SNES, matrix-free, parameters

See Also

MatCreateSNESMF(),MatMFFDGetH(), MatCreateMFFD(), MATMFFD
MatMFFDSetHHistory(), MatMFFDResetHHistory()

Level:advanced
Location:
src/mat/impls/mffd/mffd.c
Index of all Mat routines
Table of Contents for all manual pages
Index of all manual pages

-mat_mffd_err <error_rel> - Sets error_rel